1. Field of the Invention
The present invention relates to the field of apparatus and devices for the delay of electromagnetic signals. More particularly, the present invention relates to electromagnetic delay lines typically formed as printed circuits. It also relates to distributed delay lines for handling high speed signals, such as those having a rise time equal to or less than one nanosecond.
2. Description of the Prior Art
Prior art recognizes the usefulness of applying RF delay lines in radio-electronics and high speed computers to align the relative timing of electronic pulses. Delay lines with an anomalous characteristic, in which the delay time decreases with increasing frequency, also are used for sharpening (compressing) radio frequency pulses.
A simple method used to implement a delay line is to insert a length of standard 50 ohm transmission cable in series with the line carrying the signal to be delayed. This works well, but takes up a large amount of space. As commercially available components, radio frequency delay lines are typically implemented as coils connected in series or by microstrip deposition on a printed circuit board, see E. F. Bayev and E. I. Burylin, xe2x80x9cMiniature Electrical Delay Linesxe2x80x9d, Sov. Radio: Moscow, 1977 (in Russian).
Reductions in physical size have allowed the manufacture of standard delay line components which can be inserted into a printed circuit board. Using a two-conductor transmission line in which one conductor has a pattern, as the spiral pattern of FIG. 1 or the meander line of FIG. 2, and the other conductor is a ground plate, increases the delay time in such devices. The patterned conductors (spiral, meander, zigzag, or other pattern) are called impedance conductors. Selecting a high permittivity (or dielectric constant) material to be adjacent to the impedance conductor further increases the delay time. In order to provide a delay time exceeding one nanosecond, while retaining relatively small dimensions for the delay line, the relative permittivity of the high permittivity material (e.g.: the circuit board) should be as high as 60-100.
In addition (or alternatively) to increasing the transmission line length or adding an adjacent high permittivity material to increase delay time, the delay time also can be increased by using a high permeability material for the conductors which form the delay line, see U.S. Pat. No. 6,154,104 xe2x80x9cHigh permeability tapped transmission linexe2x80x9d, Hall; Garrett W. The high permeability and high permittivity materials, as taught in Hall, serve to allow an increase in delay time for a given size. This differs from the present invention, however, in that specific physical arrangements among impedance conductors to achieve another method for increased delay time are taught in the present invention.
In the prior art, delay time td is a function of the path s along the conducting elements forming the pattern, the relative permittivity xcex5r of the adjacent material between the conductors, and the relative permeability xcexcr of the outside impedance conductor. Approximately, this relationship follows the general formula:                               t          d                =                                            s              ⁢                                                                    ϵ                    r                                    ⁢                                      μ                    r                                                                                      3              ·                              10                8                                              ⁢                      xe2x80x83                    ⁢                      sec            .                                              (        a        )            
Conventionally, the pattern formed by the impedance conductor of a delay line can be described as a row of conducting members connected in series and spaced with pitch h in the direction of signal propagation, said conducting members being inclined with respect to the direction of signal propagation. The direction of signal propagation can be radial or longitudinal. The pattern can be characterized by width H or perimeter p equal to 2 xcfx80r for a regular flat spiral (where r is the radius of the spiral), and by period T or pitch h. In a meander line, the period T is equal to 2 h.
According to the definitions mentioned above, formula (a) can be rewritten for a homogeneous delay line as:                                           t            d                    =                                                                      N                  0                                ⁢                                                                            ϵ                      r                                        ⁢                                          μ                      r                                                                                                  3                ·                                  10                  8                                                      ⁢                          xe2x80x83                        ⁢            l            ⁢                          xe2x80x83                        ⁢                          sec              .                                      ,                            (        b        )            
where l is the delay line""s length, and N0 is the geometric deceleration defined for a meander line as (H+h)/h.
In an inhomogeneous delay line, such as a flat spiral, the delay time can be calculated by the formula:                                           t            d                    =                                    1                              3                ·                                  10                  8                                                      ⁢                                          ∑                1                n                            ⁢                              xe2x80x83                            ⁢                                                p                  i                                ⁢                                  xe2x80x83                                ⁢                                  sec                  .                                                                    ,                  xe2x80x83                ⁢                  i          =          1                ,        2        ,        3        ,        …                            (        c        )            
where pi is the perimeter (length) of the winding, and n is the number of windings
For a regular radial spiral, the relationship is:                               t          d                =                              ∫                          r              1                                      r              2                                ⁢                                                    2                ⁢                                  xe2x80x83                                ⁢                π                ⁢                                  xe2x80x83                                ⁢                r                ⁢                                                                            ϵ                      r                                        ⁢                                          μ                      r                                                                                                                    3                  ·                                      10                    8                                                  ⁢                                  xe2x80x83                                ⁢                h                                      ⁢                          xe2x80x83                        ⁢                          ⅆ              r                        ⁢                          xe2x80x83                        ⁢                          sec              .                                                          (        d        )            
where r1 is the minimum, and r2 is the maximum radius.
However, when a delay line is constructed with high permeability or high permittivity materials for the base element and layers adjacent to the impedance conductor, additional electromagnetic signal dissipation is caused by the losses in the base and layers. For delay times exceeding 10 nanoseconds, these losses are very large. Frequency dependence (shape) of the attenuation factor also changes the configuration (shape) of the signal. Temperature dependence of permittivity and permeability of these materials is large, which leads to variation in the delay time with changes in temperature. Also, high permittivity and high permeability materials are expensive.
To achieve a delay time exceeding 10 nanoseconds while preserving the signal amplitude and configuration, additional deceleration of the signal should be obtained without increasing the conductor length, the permittivity, or the permeability of the materials. Thus, there is a need in the art for a new way to design delay lines with small dimensions, small electromagnetic losses, and high delay time.
In U.S. Pat. No. 4,570,136, xe2x80x9cElectromagnetic Delay Linexe2x80x9d, Kameya, Kazuo, a microstrip delay line with electromagnetic coupling between the individual conducting elements of the same electrodynamic structure is shown. This differs from the present invention in that Kameya teaches an increase in delay time which is caused by the displacement of the conducting elements in the transverse direction. This adds to complexity of construction, and the increase in delay time is not significant when compared to the greater increase in delay time which is achieved by using the present invention. The present invention teaches a greater increase in delay time without an increase in complexity of construction.
In contrast to prior art delay line components, the present invention provides a novel method for increasing the delay time, reducing the physical size, or adjusting the signal configuration. In addition to the prior art methods of path length, permeability of the impedance conductors, and permittivity of the adjacent material, the present invention teaches constructions which accomplish this through interaction of electromagnetic fields.
Both the prior art and the present invention provide for the delay of an electromagnetic signal. The present invention and some of the prior delay lines use a dielectric base, such as a printed or multi-layer circuit board, and at least two conductors forming a transmission line.
It is an object of the present invention to create a distributed delay line, which provides a delay time exceeding the delay time defined by geometric deceleration and materials of construction, including materials of high permeability and high permittivity.
It is a further object of the present invention to provide a distributed delay line, which is easy to manufacture and is economical.
It is a further object of the present invention to provide a distributed delay line, having a delay time which has reduced temperature sensitivity.
It is a further object of the present invention to provide a simple distributed delay line, with an anomalous dependence of the delay time upon frequency.
It is a further object of the present invention to provide a distributed delay line which has small electromagnetic losses.
It is yet a further object of the present invention to provide a distributed delay line which can be used to control the configuration of an output signal.
According to the most general aspects of the present invention, these objectives are accomplished by distributed delay lines comprising at least one non-conducting base and at least two conductors which face one another, thus forming a transmission line with at least two input terminals and at least two output terminals. The signal is delayed between the input terminals and the output terminals of the delay line. The delay time is greater than the delay time achieved in prior art. This is accomplished by forming at least two of the adjacent conductors as rows of conducting members arranged in series with pitch h. The pitch is in the direction of signal propagation. The adjacent conductors are connected to one another with spacing. The conducting members are inclined to the direction of the signal propagation, with conducting members of different impedance conductors facing one another being inclined in opposite directions (e.g. clockwise and counterclockwise).